The invention relates to a method of identifying a desired path for a user information signal between a first and second apparatus in a system of three or more apparatuses, the apparatuses of the system being interconnected on a one-to-one basis for the transmission of user information signals while being connected to a serial data bus having distributed control, the method comprising:
(a) initiating a first autonomous process whereby, using a sequence of data bus messages and starting from the first apparatus, a succession of one-to-one connections are identified through a succession of apparatuses of the system until the second apparatus is reached. PA1 (b) initiating concurrently with the first autonomous process a second autonomous process whereby a succession of one-to-one connections are identified, starting with a third apparatus, through a succession of apparatuses of the system until the second apparatus is reached; and PA1 (c) in the event that the third apparatus is reached at an intermediate stage in the first process terminating the first process and appending the path identified by the second process to the path identified so far by the first process. PA1 means for receiving information that a signal path is desired to be identified between a first and a second apparatus of the system; PA1 means for initiating a first autonomous process whereby, using a sequence of data bus messages and starting from the first apparatus, a succession of one-to-one connections are identified through a succession of apparatuses of the system until the second apparatus is reached; PA1 means for initiating concurrently with the first autonomous process a second autonomous process whereby a succession of one-to-one connections are identified, starting with a third apparatus, through a succession of apparatuses of the system until the second apparatus is reached; and PA1 means operative in the event that the third apparatus is reached at an intermediate stage in the first process for terminating the first process and appending the path identified by the second process to the path identified so far by the first process.
The invention further relates to a signal processing apparatus for implementing such a method in a system of interconnected apparatuses.
Such a method is known from GB 2 223 114 A (PHN 12678), the contents of which are hereby incorporated by reference. Apparatuses including control means for implementing the known method using a domestic digital bus (D2B) are for example Philips' colour television model 2070 and video cassette recorder (VCR) model VR6590. The serial data bus has many applications besides the present method, and it is desired that a standardised set of application protocols be developed and adhered to by many manufacturers of consumer audio/video apparatus, so that a data bus such as D2B can provide enhanced functionality and user friendliness to the great variety of apparatus types available today and in the future, with true inter-brand compatibility.
To this end, and with a view to minimising the cost and complexity of compatible apparatuses, it is a principle of the known system that any apparatus (addressable via the bus as a `device`) knows only whatever is needed for its own functionality. For example, after an initialization phase, each device knows (only) its own logical connections and the physical connections of its external plugs. Thus in the known method, the autonomous process referred to is performed step by step under the control of the various devices involved. At the end of the process, the information about the topology of the path connecting the first and second devices is not stored in any central location, but all local connections are known by the devices involved.
It is clearly desirable that a signal path should be established in response to a user command without any perceptible delay for the user. However, in a large system, it has been found that delays can become excessive due to the long sequence of local interactions necessary for exploring the network and confirming the success or failure of the method under local control.
It is an object of the invention to reduce the delay involved in identifying a signal path while remaining compatible with existing apparatus and while adhering to the principles set forth above.